1. Field of the Invention
The present invention relates to a color filter manufacturing method using dry etching process.
2. Description of the Related Art
Dyeing, printing, electrodeposition and pigment dispersion methods have been known as methods for fabricating color filters for use in liquid crystal display devices or solid-state image sensors.
Of these methods, pigment dispersion method is to fabricate color filters by photolithography process using a radiation sensitive colored composition which is prepared by dispersing a pigment in one of various types of photosensitive compositions. This method offers the advantage of having good stability to light and heat because it uses a pigment. Furthermore, the method ensures high positioning accuracy because it employs photolithography process for patterning; therefore, it has been widely used as a suitable method for fabricating color filters for use in large-size and high-definition color displays.
In the case that a pigment dispersion method is employed for color filter fabrication, color filters can be obtained by: first applying a radiation sensitive composition onto a glass substrate with a spin coater or roll coater, followed by drying to form a film on the glass substrate; second subjecting the formed film to pattern exposure/development to form colored pixels; and repeating these operations for each color.
There are described in some documents examples of the foregoing types of pigment dispersion method which uses a negative-type photosensitive composition prepared using an alkali-soluble resin together with a photopolymerizable monomer and a photopolymerization initiator (e.g. Japanese Patent Application Laid-Open Nos. 2-181704, 2-199403, 5-273411 and 7-140654).
To cope with the demands for higher-quality images of color filters, which cannot be realized with the foregoing negative-type photosensitive composition, there are described in some documents another type of pigment dispersion method which aims at providing color filters whose pixels have been controlled to have desired size and shape and uses a negative-type photosensitive composition prepared using, as an alkali-soluble resin, an acrylic resin having per molecule an alkylene oxide chain and/or hydroxyethyl methacrylate (HEMA)(e.g. Japanese Patent Application Laid-Open No. 2005-326453).
In the mean time, color filters for use in solid-state image sensors have recently been desired to have higher definition. In solid-state image sensors, fine size-reduction is noticeable, and high-resolution technology capable of providing resolution less than 2.0 μm in size has been needed; thus, the resolving power of current photolithography almost reaches its limits.
Besides the foregoing color filter fabricating methods, which use photolithography process, there are color filter fabricating methods using dry etching process, which has been long known as an effective process for forming a thinner and fine pattern. Dry etching process has been conventionally employed as a process for forming a pattern on a vapor-deposited thin film of a pigment (e.g. Japanese Patent Application Laid-Open No. 55-146406). The process is capable of forming a thin film whose thickness is half or less of that of the thin film formed by photolithography process while keeping the spectral characteristics of the thin film almost the same as those of the thin film formed by photolithography process. There are also proposed pattern forming methods which use photolithography process and dry etching process in combination (e.g. Japanese Patent Application Laid-Open No. 2001-249218). Furthermore, there are proposed techniques for making photoresist stripping easy in which the damage surface layer, caused by etching, of photo resist is removed by ashing (e.g. Japanese Patent Application Laid-Open No. 2003-332310).
In manufacturing of color filters using dry etching process, usually the problem of support damage (shaving) caused by over-etching treatment tends to occur. For example, when intending to form a pattern by removing the colored layer on a support by dry etching, part of the support in the area where the colored layer has been removed is sometimes shaved, thereby causing unevenness on the support. Or, over-etching treatment is sometimes carried out after detecting the end point of etching to remove residues on a support, in that case, when an organic film exists on the support or etching gas containing fluorine-based gas is used, it is difficult to avoid the occurrence of support damage.